\begin{tikzpicture}
    \pgfmathsetmacro{\R}{2}
    \begin{scope}
        \coordinate (O) at(0,0);
        \draw (O) circle [radius=\R];
        \draw (O) -- (90:\R);
        \draw (O) -- (210:\R);
        \draw (O) -- (330:\R);

        \draw (-0.8,  0.8) node [align=center] {锐角\\[-0.5em]三角形};
        \draw ( 0.8,  0.8) node [align=center] {钝角\\[-0.5em]三角形};
        \draw (   0, -0.8) node [align=center] {直角\\[-0.5em]三角形};

        \draw (0, 2.5) node {按角分};
        \draw (0, -2.5) node {三角形集合};
    \end{scope}

    \begin{scope}[xshift=6cm]
        \coordinate (O) at(0,0);
        \draw (O) circle [radius=\R];
        \draw (90:\R) -- (270:\R);

        \pgfmathsetmacro{\r}{0.8}
        \coordinate (O') at(-\R/2,0);
        \draw (O') circle [radius=\r];

        \draw (-0.8, 1.3) node [align=right]  {等腰\\[-0.5em]三角形};
        \draw (\R/2, 0)   node [align=center] {不等边\\[-0.5em]三角形};
        \draw (O')        node [align=center] {等边\\[-0.5em]三角形};

        \draw (0, 2.5) node {按边分};
        \draw (0, -2.5) node {三角形集合};
    \end{scope}
\end{tikzpicture}

